Neuromuscular electrical stimulation (NMES) involves the controlled stimulation of muscular nerve centers. Known uses of NMES include, for example, the diagnosis of chronic pelvic pain and the installation of a system to produce an effective cough mechanism.
It may be desirable to use minimally invasive surgical techniques for NMES. A minimally invasive NMES apparatus 10 that is known in the prior art is shown schematically in FIGS. 1 and 2. This apparatus 10 includes the cannula portion 12 of a trocar system. The cannula 12 is shown in an operative position in which it extends through an incision 15 in a patient's abdominal wall 16 to communicate the internal peritoneal space 19 with the adjacent external space 21 in the operating room. A trocar (not shown) is first moved through the cannula 12 and pressed against the outer surface of the abdominal wall 16 to form the incision 15 in a known manner. The cannula 12 is then advanced through the incision 15. The apparatus 10 further includes a mapping probe system 30 which is shown in an operative position extending through the cannula 12 from the external space 21 into the peritoneal space 19.
The mapping probe system 30 includes a rigid metal tube 32 which is inserted through the cannula 12 after the trocar is withdrawn from the cannula 12. A flexible plastic tube 34 is then inserted through the rigid metal tube 32. The inner end of the flexible tube 34 is equipped with a contact electrode 36. The outer end of the flexible tube 34 is connected to an operating room vacuum.
As shown in FIG. 2, the electrode 36 is a suction tip electrode. Accordingly, it has an internal passage 37 that serves as a suction port 37 to enable suction in the flexible tube 34 to hold the electrode 36 temporarily against an internal surface at a test site, e.g., a phrenic nerve motor point on the diaphragm muscle. An electrical wire 38 in the flexible tube 34 is part of a known stimulator system that connects the electrode 36 in a pair with a remote electrode (not shown) to provide NMES for characterization and mapping of the electrical response at the internal test site.
As known in the art, the patient's abdomen is inflated by gas pressure provided in the peritoneal space 19. As further known in the art, the cannula 12 grips the rigid tube 32 to form a pneumatic seal that blocks leakage of the inflation gas along a path extending outward through the cannula 12 between the outer surface of the rigid tube 32 and the surrounding inner surface of the cannula 12. The rigid tube 32 is rigid enough to withstand the grip of the cannula 12 without collapsing, but the flexible tube 34, which can bend under the influence of the moving diaphragm muscle, is not. As shown in FIG. 2, a small gap exists between the outer surface 42 of the flexible tube 34 and the surrounding inner surface 44 of the rigid tube 32. This gap provides a flow path that enables the inflation gas to leak from the peritoneal space 19 without passing through the suction-tip electrode 36.